The determination of mass composition can also be pursued using the SD by measuring the number of muons of the EAS that reach the ground. This detection possibility is affected by larger uncertainties respect to the \(X_{max}\)  observation, due to theoretical unknowns in the hadronic physics at the highest energies of the EAS development. Experimentally, both Auger and TA observe a mismatch between the number of muons observed with energies above \(10^{9.5}\)  GeV and the number of muons predicted by the EAS models [1]}, [2]}.
